The track size of a recording bit becomes finer with increasing memory density of a magnetic disc apparatus, and therefore, further high sensitivity is required of a magnetic playback head. In particular, in recent years, a magnetic playback head using a tunnel magnetoresistive effect (TMR) film has received attention as a next generation ultra-sensitive magnetic sensor as described in the document 1 (NIKKEI Electronics, No.774 (Jul. 17, 2000), pp. 177–184).
In this document 1, a structure of a read head is disclosed, wherein laminated layers consisting of a bottom magnetic shield, a soft magnetic free layer, a nonmagnetic insulator, a ferromagnetic fixed layer, an antiferromagnetic layer fixing the magnetization direction of a ferromagnetic fixed layer, and an electrode are formed in order on a bottom magnetic shield and then patterned. And it comprises a hard magnetic metal layer placed at both ends of the laminated layer to fix the magnetization direction and an insulating layer to insulate said top magnetic shield and bottom magnetic shield.
In addition, recently, a new type of TMR sensor was proposed as a sensor using the TMR effect as described, for example, in the document 2 (Nature, Vol. 416, pp. 713–715, 2002), wherein two laminated layers of insulator/ferromagnetic metal were formed at different positions of an Al metallic electrode layer, a current passed from said first ferromagnetic layer to said Al electrode, a polarized spin diffused to the Al electrode underneath another laminate layer of insulator/ferromagnetic metal, and a change in resistivity detected by changing the magnetization direction of the second ferromagnetic layer.    [Non-patent document 1] NIKKEI Electronics, No.774 (Jul. 17, 2000) pp. 177–184    [Non-patent document 2] Nature, Vol. 416, pp. 713–715, 2002